(a) Field of the Invention
The present invention relates to a concentration ratio controlling apparatus for concentration type solar cells that may be mounted to a solar simulator used to measure a photoelectric conversion characteristic of a concentration type solar cell to thereby adjust a concentration ratio of sunlight to be a predetermined value.
(b) Description of the Related Art
Currently, people are facing problems such as a serious level of air pollution, depletion of natural resources, and the like. Due to depletion of resources and an increase in resource prices, research and development of clean and new renewable energy has been actively conducted. Examples of the clean and new renewable energy may include solar energy, wind energy, tidal energy, and the like. In particular, to efficiently use the solar energy, research and development of a solar cell has been continuously performed.
Even though a variety of materials have been developed to be used as a solar cell material, a single-crystalline silicon solar cell has been generally in the mainstream so far. Solar cells using polycrystalline silicon, amorphous silicon, a III-V compound semiconductor, a thin film type solar cell (copper-indium-gallium-selenide (CIGS)), a dye-sensitized material, and the like, in addition to single-crystalline silicon, have been developed. Among the various solar cells, a concentration type III-V compound semiconductor solar cell has been reported to have the most excellent efficiency while showing the photoelectric conversion efficiency of greater than or equal to 40%.
A concentration type solar cell decreases a system cost by using only a small size of an expensive solar cell and instead, applying an optical lens (Fresnel lens) and the like, thereby concentrating the sunlight to a solar cell. Even a silicon solar cell may concentrate light. However, silicon is an indirect transition type semiconductor and thus, when a temperature increases, the efficiency decrease sensitively. Accordingly, the silicon solar cell is used only for concentration of up to about 20 folds to 100 folds. The silicon solar cell may use concentrate light even over 100 folds. However, in this case, it is known that a device production cost increases and thus, there is no great return.
Unlike this, the III-V compound semiconductor has an excellent high temperature characteristic and excellent temperature stability and reliability, and also has a characteristic in which photoelectric conversion efficiency increases according to concentration. Accordingly, the III-V compound semiconductor is most suitable for a high concentration type photovoltaic system. In the case of a III-V compound semiconductor multi-junction solar cell, a highly efficient solar cell having the high photoelectric conversion efficiency of greater than or equal to 40% (40.7%, U.S.A. Spectrolab) has been currently developed. High magnification concentration of greater than or equal to 500 folds is possible. In the European countries, research on concentration of greater than or equal to 1000 folds is also ongoing. In the U.S.A., the European countries, and Japan, a variety of investments have been made in the field of the III-V compound semiconductor solar cell in the meantime. Currently, many researches are ongoing in order to develop a concentration type solar cell and a highly efficient solar cell.
A solar cell is an apparatus for converting optical energy of the sun to electrical energy. The solar cell has competitiveness when the solar cell has high efficiency in the case of the same area and a production cost is low. However, the concentration type solar cell using the III-V compound semiconductor or the silicon material is predicted to be capable of satisfying the above conditions and thus, many researches thereon are ongoing. It is known that the III-V compound semiconductor has an excellent high temperature characteristic and excellent temperature stability and reliability, and also has a characteristic in which photoelectric conversion efficiency increases according to concentration and thus, is most suitable for a high magnification concentration type photovoltaic system.
However, there is a limit in adjusting the quantity of light of a lamp that is a light source in order to concentrate light to be greater than or equal to 1 Sun (100 mW/cm2), which is generally used, or to irradiate weak light to be less than or equal to 1 Sun by employing a solar simulator or an artificial solar test apparatus used to measure a characteristic of a solar cell indoors.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.